In the prior art press, dynamic balance of the inertia force is maintained between a slide which moves vertically and a crankshaft which rotates eccentrically, the balance being maintained by means of balancing weights moving relative to the crankshaft or a slide movable via gears, levers, or links. This arrangement has made the whole structure large and complex and has presented many difficulties.
The present inventor has proposed a means to solve the defects of the prior art balancing means in Japanese Patent No. 60-180699.
The proposed means is characterized in that a connecting rod is fitted to the eccentric part of the crankshaft of the press, a link is attached to the head of the connecting rod, a pair of balancing weights are provided on both sides of the crankshaft near the center thereof in a manner so as to be movable in a direction opposite to the direction of movement of the press slide, and levers connected to the upper end of each balancing weight overlap at the center of the slide and are connected with the link, the levers being pivoted to the frame of the press at their mid-portion.
The above described means is superior to the prior art devices in that the balancing weights are provided inside the frame of the press, allowing effective use of the cavity space, and in that the construction is simple and compact. It is defective, however, in that because the levers connected to the balancing weights and the connecting rod connected to the slide are connected by means of a link, the point where the slide and the link member are balanced does not coincide with the axial center of the crankshaft, making the balance not quite perfect, and even defective.